The invention relates generally to cutters, downhole cutting tools that employ such cutters, including arms and blades of underreamers, mills and other downhole cutting tools and methods of making the same.
Rotary cutting mills, mandrel cutters and the like are downhole cutting devices or tools that are incorporated into a drill string and used to cut laterally through metallic tubular members, such as casing on the sides of a wellbore, liners, tubing, pipe or mandrels. Mandrel cutters are used to create a separation in metallic tubular members. Cutting mills are tools that are used in a sidetracking operation to cut a window through surrounding casing and allow drilling of a deviated drill hole. On conventional tools of this type, numerous small individual cutters are attached to multiple arms or blades that are rotated about a hub. Most conventional cutters present a circular cutting face. Other conventional cutter shapes include square, star-shaped, and trapezoidal, although these are less common.
Improved cutter designs and improved designs for downhole cutting tools that use them, such as mandrel cutters and rotary cutter mills, having a rectangular, rounded “lozenge” shape have been proposed. This cutter has a cross-sectional cutting area having a pair of curvilinear end sections an elongated central section with a length that is greater than the width. The cutter may also include a raised peripheral cutter edge for breaking chips during cutting. Cutters of this type have an improved geometry over circular cutters, and particularly have reduced interstitial space as compared to circular cutters. While these lozenge shape cutters have reduced interstitial spaces associated with adjacent cutters, they have a relatively higher amount of total surface area that requires bonding to the cutting tools on which they are employed. This bonding is generally accomplished by brazing the lozenge shape base of the cutter to the desired cutting surface of the cutting tool. The relatively higher amount of total surface area of the cutters may increase the potential for defects in the braze joints between the cutters and the cutting tools.
Thus, in addition to realizing the performance benefits of the cutters described, an improved metallurgical bond to their enhanced surface area is desirable.